Taiwan has submitted its first formal application to join the United Nations, a government spokesman has said.
He said an application signed by President Chen Shui-bian had been delivered to the UN Secretary General.
The Chinese foreign ministry immediately dismissed the move, saying it was "doomed to failure".
Taiwan has long campaigned to join the UN but all such attempts have been blocked by China which regards the island as a breakaway province.
The government in Taipei held the UN seat for China until 1971 when it was replaced by Beijing.
This was the first time the country launched a bid for UN membership using its own name rather than the official title "Republic of China" used in earlier attempts.
"We resolutely oppose it and will keep a close eye on the development of the issue," Chinese foreign ministry spokesman Liu Jianchao was quoted as telling Xinhua news agency.
"The Taiwan authorities' attempt to split China will absolutely not succeed," he added.
China has claimed sovereignty over Taiwan since nationalist armies fled the mainland following defeat in a civil war in 1949.
Taiwan is officially recognised by just 24 countries around the world.